The Bureau of Standards experimental radio station, WWV, was first set up in 1919.
Radio News, August, 1920, page 75:

Music  Wherever  You  Go

Government  Experts  Develop  a  Portable  Radiophone

HERE is the last word embodied in the portable receiving set idea. This highly efficient instrument has been developt in the radio section of the Bureau of Standards at Washington and altho the experts of this Bureau modestly referred to it as being in the experimental stage, it is probable that this type of instrument is destined to become widely used on account of its practical and portable nature.
    The present portaphone has one stage of radio amplification and two stages of audio amplification; one tube being used both as a radio and audio amplification stage. portaphone
    By referring to the left hand illustration of the above photograph, which shows the internal construction of the set, may be seen the loop which is wound upon the four sides of the cover. Directly in the center of this cover is the tunmg condenser for wavelength variation. The instrument, by the way, was designed to receive waves of 500 meters. The vacuum tubes are of a special design requiring but 0.2 ampere to operate the filament. It will also be noted that both the A and B batteries are conveniently arranged within the case, they being as small and compact as possible in order to secure minimum weight for the entire unit. It will be seen that the amplifying transformers are at right angles to each other in order to eliminate all possible mutual, effects between individual circuits.
    When the radio telephone station of the Bureau of Standards at Washington is in operation with an antenna current of 2 amperes while transmitting, music and speech may be readily picked up by a person situated, within the city limits by using the portaphone.
    The instrument itself without the horn is 12" high and 10" wide. This gives an idea of its compactness and portable nature. The horn, of course, may be strapt to the case and carried along as well. A desirable feature connected with the instrument is that it is very simple of operation and does not require an expert electrician or radio wan to set it in operation. This fact alone opens up considerable future possibilities in the commercial field. Incidentally, it would be an ideal set for the more advanced amateur to take along with him on his vacation, be it far into the mountains or at the seashore. He thus can keep in touch with the news, weather reports, radiophone conversations, radiophone music, and any other information transmitted by radio,
    The approximate range of the instrument in its present development is about 20 miles, but of course this can be considerably increased by making use of a regular antenna. An instrument similar to this one has been built at the radio section of the Bureau of Standards which is sufficiently powerful as a transmitter to reproduce phonograph or other music with enough intensity so as to be heard within a room of considerable size and which, by the way, would be an excellent arrangement for dancing.
    A more sensitive type of portaphone is now under construction by the Government experts. It will contain three radio and two audio stages of amplification and will be so arranged that the horn and all other instruments are self-contained within the box. With this device music may be heard within the limits of any large city.